Thin film transistors (TFTs) have been widely used as pixel switching elements for displays, such as liquid crystal displays and EL displays. Also, examples in which the driver circuit for the pixel array is also formed by a TFT on the same substrate have increased in recent years. Such TFTs have been conventionally made on a glass substrate, using amorphous and polycrystalline silicon.
However, problems have been that CVD apparatuses used for making such TFTs using silicon are very expensive, and that a larger area of displays and the like using TFTs involves a significant increase in manufacturing cost. Also, since the process of forming a film of amorphous or polycrystalline silicon is performed at very high temperature, there has been such a restriction that materials that can be used as the substrate are limited, and lightweight resin substrates and the like cannot be used.
TFTs using a CNT-dispersed film as the semiconductor material have been proposed as means for solving such problems. The CNT-dispersed film is usually formed by a wet process, such as application. This process has such advantages that a larger area can be achieved at low cost, and that restrictions in selecting a material used as the substrate are few because the process temperature is low. Therefore, the practical use of the TFTs using the CNT-dispersed film has been expected. In fact, the TFTs using the CNT-dispersed film have been frequently reported in recent years, and there are examples of reports, such as Non-Patent Documents 1 to 4.    Non-Patent Document 1: E. S. Snow, J. P. Novak, P. M. Campbell, D. Park, Applied Physics Letters, Vol. 82, p. 2145, 2003    Non-Patent Document 2: E. Artukovic, M. Kaempgen, D. S. Hecht, S. Roth, G. Gruener, Nano Letters, Vol. 5, p. 757, 2005    Non-Patent Document 3: S.-H. Hur, O. O. Park, J. A. Rogers, Applied Physics Letters, Vol. 86, p. 243502, 2005    Non-Patent Document 4: T. Takenobua, T. Takahashi, T. Kanbara, K. Tsukagoshi, Y. Aoyagi, Y. Iwasa, Applied Physics Letters, Vol. 88, p. 33511, 2006